1. Field of the Invention
The invention relates to a method for preventing pathogens from mutating caused by overexpression of transgenes in genetically-modified or transgenic plants.
2. Description of the Related Art
Agriculture relies on a comprehensive and complicated equilibrium, which when disturbed has often unintended effects. For example, it is well-known that excessive application of pesticides to crops results in pesticide resistance of pest and pathogens, i.e., the adaptation of pest and pathogen species targeted by a pesticide resulting in decreased susceptibility to the pesticides applied. In other words, pests develop a resistance to the applied pesticide through artificial selection; after they are exposed to a pesticide for a prolonged period it no longer kills them as effectively. The most resistant organisms are the ones to survive and pass on their genetic traits to their offspring. Similar to pesticide resistance is the phenomenon of transgenic resistance, wherein pests and pathogens become resistant via mutation pathways to transgenic plants and toxins overexcreted by transgenic plants.
It is estimated that the cost of creating pathogen-resistant transgenic crop varieties is at least several hundred thousand dollars per variety. Even so, the high cost does not guarantee predictability. In addition, resistance genes with unusually high intensity will put great specific selection pressure on targeted insects or microbes and will usually lead to endogenous mutation of those organisms. Consequently, the plants will lose their resistance or they will be infested by new pests and diseases. In such cases, new genes have to be discovered and cloned all over.
According to a report in China Science Times, transgenic Bt cotton once displayed good resistance in the field, particularly in the first 3 years of production, but subsequently, the effect began to decline or was even reversed. In the fourth year, the production cost was increased threefold and farmer's income was reduced by 8%. After having been planted consecutively for 7 years, the Bt cotton was plagued by other new insects. As pesticide application had to be increased and the cost of seeds was increased compared to non-transgenic varieties, the income of farmers was reduced.
Prolonging the application duration of transgenic plants and preventing pests and pathogens from mutation caused by them have become a key and unavoidable problem in the field of transgenic engineering. Horizontal resistance in transgenic plants can be obtained via the plants own diversified sources of transgenes. Such resistance would not exert specific selection pressure on pests and pathogens. Plants could display resistance to any possible pests and diseases and may prevent the rampancy of a certain pests and diseases. Thus, resistance duration of transgenic plants can be prolonged greatly and this will benefit the sustainable development of agriculture. Up to now, the bio-safety of gene transfer technology has not been fully confirmed. Enormous and unpredictable risks and threats cannot be excluded for the promoters of transgenes, the expression of foreign genes and possible escape of transgenes. If those cases really happen, large losses for the entire industry and great social consequences may occur.